Bishop Master Finishes Waterstone Polished Plaster | White 59, Waterstone Polished Plaster is a wall finish made up of lime putty, selected marble dust and sand aggregates. Bishop Master Finishes have created a 1-2mm thick contemporary Italian hi lustre wax polish using coloured pigments from around the world. Waterstone Polished Plaster can be applied to bare plasterboard, MDF and previously painted surfaces to create a traditional Italian Waxed Buffed Plaster Finish.